High speed relay of electromechanical transducer material



Aug. 2, 1955 T. G. KlNsLEY 2,714,642

HIGH SPEED RELAY OF ELECTROMECHANICAL. TRANSDUCER MATERIAL Filed July10, 1952 s Sheets-Sheet 1 III Aug. 2, 1955 r. G. KINSLEY HIGH SPEEDRELAY OF ELECTROMECHANICAL TRANSDUCER MATERIAL 3 Sheets-Sheet 2 FiledJuly 10, 1952 //Vl/E/V7'OR 7? G. K/NSLEV B) 2 A4. ATTORN V 2, 1955 T. G.KINSLEY 2,714,642 l HIGH SPEED RELAY OF ELECTROMECHANICAL TRANSDUCERMATERIAL Filed July 10, 1952 3 Sheets-Sheet 3 //v l E/V TOR y 7. G.K/A/SL E V ATTOR/VE tice IVIATERIAL Thomas G. Kinsley, Plait-afield, N.l, assi or to Bell Telephone Laboratories, incorporated, New York, N.Y., a corporation of New York Ap lication an it 1e52, Seriai No. 298,114

This invention relates to electromechanical relays and, moreparticularly, to relays in which movement is dependent upon theelectrostrictive or piezoelectric characteristics of anelectromechanical transducer element.

One of the objects of the invention is to increase the speed at whichthe movable element of such a relay responds to the application orremoval of the operating voltage.

A further object of this invention is to extend the motion of thetransducer elements and to insure high speed operatin stability whileyet retaining a simple and rugged construction.

Still another object is to provide for operation of such a relay over abroad band of actuating current frequencies.

In accordance with a feature of the invention, a transducer element ismounted on elastic strips which act not only as mounting means and serveto constrain the motion of the element at its edges, but also toactively contribute to the motion of the transducer element.

Another feature of the invention is the critical placement of dampingmeans against the movable element of the relay that absorbs theinterference from spurious modes of vibration and adds to the edgestilfness of the movable element.

In accordance with the present invention, a relay is formed of a centerfiexure plate, with a relay contact of a contact pair on one face of theplate, and a supporting structure for the fiexure plate that permits thecontacts to close with the flexing of the plate and which structuresubstantially increases the all too limited motion that 4;, can beachieved with the flexure plate alone.

In a specific embodiment of this invention, the fiexure plate is abimorph ceramic disc of two joined polarized electrostrictix etransducer elements such as barium titanate. In an instance where eachelement is 2 inches in diameter and 10 mil inches thick and is polarizedin its radial mode, the measured center displacement of the disc is only1.3 mil inches when 200 volts is applied to one disc. In this inventionall of the center displacement motion of the disc is not only preservedbut it is substantially contributed to by the mounting means. The discis attached to a backing plate, which is one extension of the mountingstand, with three elastic shaped mounting strips that are connected tothe disc at equally spaced intervals around its edge. The mountingstrips are made of a resilient element such as annealed beryllium copperand have two sharp bends which are weakened to permit the bends to serveas elastic hinges about which motion is directed permitting movement ofthe center flexure disc in limited paths. Further, each strip is soshaped that it selectively resists longitudinal displacement of theperiphery of the disc, provides a stable platform for the disc fromwhich all longitudinal center displacement may be measured, and alsoprovides lever arms which, when called into motion by the forcesoperating near the periphery of the flexing disc, lift the disc inrhythm with the flexing action to further extend the center of the discfrom its neutral position.

For such a bimorph disc of barium titanate as described above, theresonant frequency is found to be near 1600 cycles per second and thecenter displacement is maximum at that frequency.

Damping means of butyl rubber, for example, placed around the edge ofthe disc are found to add stiffness to the disc and increase theresonant frequency and also act to control any higher modes of vibrationthat appear in the disc tending to decrease its center displacement bydisrupting the primary mode of vibration. With such damping arrangementthe disc is capable of continuous operation at frequencies from zero toseven thousand cycles per second with the exception that someirregularities appear the operation at the frequencies from 3,000 to5,000 cycles per second. Additionally, adjustments in the contactspacing for changes in the center displacement of the disc do not haveto be made except near the 5,000- to 7,0G0-cycles-per-second range.

When the spacing between contacts is six tenths of the total discdisplacement distance and sufiicient contact damping is provided toabsorb the remaining disc displacement motion, a contact opening andclosing action is had that is smooth and free of any contact chatterresulting from unexpended energy stored in the actuated disc.

As limited by the physical characteristics of the bimorph itself, acenter displacement that is six tenths of the total center displacement(at which point the relay disc a resonant frequency of will occur in 100microseconds after the voltage is applied. In a relay having a singlebimorph disc, this operation time may be reduced below 100 microsecondsonly by varying the contact spacing within the limits dictated at oneextreme by the damping required to prevent contact chatter and at theother exmay be further reduced, for example, by mounting each contact ofa contact pair on separate flexure discs that have been linked forsynchronous motion.

Below the maximum operate time as limited by the physicalcharacteristics of the bimorph, its mode of motion may be furthercontrolled through the electric charge and discharge characteristics ofthe disc as influenced by the wave form of the actuating voltage appliedto the disc. Hence, an actuating voltage taking the form of a sine wavewill tend to cause moderate charge and discharge periods and moderatecontact closing and opening speeds, while a rectangular wave will tendto cause fast charge and discharge periods and fast contact close andopen speeds. By supplying actuating voltages having different Waveforms, other contact closing and opening speeds and combinations ofclosing and opening speeds may be attained.

The fiexure plate may be rectangular, circular or of any number of othergeometric shapes, but the fiexure motion is found to be high speed relaypurposes in a thin circular plate having center or diaphragm fiexuremotion. the composition of the plate may be that of a nonelasticrestraining plate of metal, plastic, or other material overlaid with andbonded to an electromechanical in the unit resulting in a flexuremotion, the most desirable composition is found to be that of anon-elastic restraining plate of electrostrictive or piezoelectricmaterial identical in physical properties to the electromechanicaltransducer overlay. A flexure plate of this bimorph disc construction,as described above, has been operated continuously in a relay that hasproven to be substantially insensitive to temperature changes over arange from 55 F. to 100 F. and remained in operating condition for weekswithout adjustment.

Polarization enhances the properties of many electromechanicaltransducers and in fact makes electrostrictive materials effectivelypiezoelectric and responsive to both positive and negative electricfields.

Where a transducer element acts as a restraining element the centerdisplacement can be substantially increased by orienting the restrainingplate to actively oppose the motion of the other element. The cumulativeeffect of such activity is a greater bending, a larger centerdisplacement of the disc, and an increased motion of the mounting leverarms which act to further extend the center of the disc from the neutralposition.

Insofar as the components of a disc can be made to grow or shrink indimensions in response to positive and negative fields, a properlyoriented bimorph disc can be made to flex in either of two directionsdepending upon the nature of the field applied. While this doubleflexure motion increases the number of modifications and adaptationsthat might be made in the specific embodiment of the invention, it doesnot necessitate a modification in the principles of elastic hingemounting that contributes to the disc displacement and the edge dampingof the disc that stabilizes higher order vibrations in the disc.

The invention, its objects and its principles will be more clearlyunderstood as hereinafter described with reference to the accompanyingdrawings showing different forms of devices suitable for the purpose.

In the drawings:

Fig. l is a sectional view of a relay having a transducer elementflexure plate in accordance with the invention;

Fig. 2 is an exploded view of the relay device according to Fig. 1showing the individual parts thereof and the manner in which they arejoined together;

Fig. 3 shows a plane view of the flexure plate and the placement of thedamping means and supporting means about the flexure plate;

Fig. 4 is a sectional view of the flexure plate and supporting meansshowing the flexure action of the hinge supporting means and thedisplacement of the flexure plate where the flexure plate is mounted forflexure in one direction;

Fig. 4A illustrates the flexing action of the hinge supporting meanswhere the flexure plate is mounted for flexure in two directions;

Fig. 5 illustrates the primary and secondary modes of motion that appearin a forced resonating transducer element; and

Figs. 6, 7, 8 and 9 are sectional views of other embodiments of a relayin accordance with the invention.

Referring specifically to the sectional view of Fig. l, a relay is shownin which a flexure plate 11, having attached thereto an electricconductive contact 12, is connected to a mounting stand 13 by mountingsprings 14 and has damping pads 15 in contact with one of its faces. Asecond electricconductive contact 16 mounted on an adjustable screw 17which is seated in backing plate 18, is spaced from and placed oppositeto the contact 12. The backing plate 18 is connected to the mountingstand 13 by adjustable bolts 19. An exploded view of the same relay isshown in Fig. 2 with a part of its composite parts identified.

The flexure plate 11, by way of example, is made up of two discs 20 and21 of barium titanate ceramic, each disc being two inches in diameterand ten mil inches thick. Disc 29 is also prepolarized in a direction ofits thickness. Electrodes 29a and 20b are, in one example, of aluminumevaporated onto the two faces of disc 20 to within forty mils of thecircumference of the disc in order to allow an electrical insulatingring around the discs edge, as shown in Fig. 3. As can be noted fromFig. 3, other portions of the disc on its outer face are left uncoatedto provide space for connecting the flexing action of the plate mountingsprings 14 and an inner electrode terminal. Such an electrode terminal22a is provided for the inner electrode Zita by a small strip ofevaporated metal which is carried from the circular electrode areaacross the insulating annulus and over the edge of the disc to its outerface where a small portion of the outer face of said disc is not coated.At the end of this strip, silver paste is fired onto the ceramic toprovide a soldering area for connecting an electric conductor to thestrip. A suitabie silver paste spot on the outer face itself constitutesterminal area 22b for the other electrode 20!) to which an electricconductor may also be soldered. The discs 2t and 21 are then cementedtogether with a thermal cement, the exposed face of disc 2% being thatone which is designated the outer face, and the entire unit is curedunder pressure.

A power source 22 shown in Fig. l is connected between the electrodesZfia and 20b at terminals 22a and 22!) so that an electric field isapplied in the same direction as the poling of the disc 20 to insurethat there will be no loss of polarization with continuous use. Theelectric conductive contact 12 is connected to a terminal 23a as shownin Fig. 4, and is cemented on and attached to disc 21 of the flexureplate 11 through an electric insulator 23.

The mounting springs 14, of which there are three to assure a flatunstressed plate, are connected to disc 20 of the flexure plate atevenly spaced intervals near the periphery, as shown in Fig. 3. Thespring 14, of which an unstressed top view is shown in Fig. 3, and anunstressed side view identified by the broken line with a stressed sideview identified by the solid line are shown in Fig. 4, is made in thisinstance of a long thin strip of annealed beryllium copper bent backupon itself at two points across its longitudinal axis through obtuse135 degrees, forming two parallel 14b joined by a middle section 140. Toadd resiliency, the shaped strip of beryllium copper is subjected to ahardening heat treatment. The exposed faces of the bends are weakened bymilling or filing for example, to form elastic pivot lines 24a and 2411so that when the end sections are stressed along the longitudinal axisof the strip all motion will be restricted to the weakened bends. Pivotline 24a divides portions 14a and 140, whereas line 24b divides portions14b and 140. With the end portion of the spring 14a attached to theflexure plate 11 and the end portion 14b firmly attached to the mountingstand 13, and the plate 11 actuated, the stress set up in the spring asa result of the will cause the portions 14a and 14c to rotate around thebend line 24b, and end portion 14a to also rotate around the bend line24a so that both obtuse angles are made smaller. The rotation of portion14a about the pivot line 2417 increases the displacement of the bendline 24a and the flexure plate supporting portion 14a from the mountingstand 13 over the measurement taken when the plate and spring isunstressed by a distance 0?. Additionally, the rotation of portion 14aaround the bend line 2411 increases the displacement of the disc fromthe bend line 24a by a distance e. Hence, the spring contributes to thedisplacement of the plate by a distance d+e, in this instance, so thatthe total displacement at the center mounted contact 12 with the plate11 mounted for diaphragm flexure in one direction is equal to the normaldiaphragm flexure displacement plus the displacement distances d-j-e.

In the case where the plate 11 is mounted for diaphragm flexure in twodirections, as shown in Figs. 8 and 9, the strip comprising the mountingspring will be bent in two places through obtuse angles only slightlygreater than degrees so that when the spring is stressed by a plateflexure in either direction, the rotation of portion 14a around 2412will be such that the distance d will be substantially zero. Hence, inthis case the spring 14 contributes to the displacement of contact 12 bya distance e as shown in Fig. 4A.

angles not greater than end sections 14a and The damping pads 15 areheld against one face of plate 11 at evenly spaced intervals between themounting springs and near the periphery of plate 11, as shown in Fig. 3,by means of adjustable screws 15a which are seated in the backing plate13. The pads themselves are made of an energy dissipating material suchas butyl rubber to damp and control the higher modes of vibration thatappear at the edge of the plate 11 as shown in Fig. 5 and also to add tothe edge stiffness of the plate. The pads in so acting tend to increasethe resonant frequency of the plate and to eliminate the vibrations thatinterfere with the primary mode of vibration.

The receiving contact 16 is formed into a shape which permits it to dampthe motion between itself and the driving contact 12 to eliminatecontact chatter which would otherwise destroy the advantages gainedthrough fast operation. As shown in Fig. 1 this is accomplished in oneinstance by soldering a six mil inch strip of palladium silver to theadjustable screw I17, bending it over in a U shape, and insertingbetween the faces of the U a piece of butyl rubber 16a. When the contactspacing is adjusted to six-tenths of the total possible centerdisplacement, the remaining motion compresses the rubber backing andreduces the kinetic energy stored in the driving unit plate 11 thecontact 16. As shown in Fig. 1, electric conductor pairs 25 areconnected to the contacts 12 and 16.

Fig. 6 illustrates another embodiment of the invention in which thespeed of operation may be increased over that of Fig. 1. Flexure and hascontact 12 attached thereto as shown in Fig. 1; and in addition, in thisembodiment contact 16 is mounted at the center of a fiexure plate 26which is a bimorph of the same construction and composition as plate 11.Plate 26 is field from source 22 connected in parallel with plate 11 sothat when the field is applied contacts 12 and 16 are displaced towardsone another. In addition, plate 26 is attached to backing plate 18 withmounting springs 14 and clamped with pads 15 in the same manner as plate11. However, in this embodiment inasmuch as two fiexure plates are used,if the gap between contacts 12 and 16 is made six tenths of the combineddisplacements of plates 11 and 26, the distance between said contactswill be approximately double that of the device shown in Fig. l but theoperate time will remain substantially the same. By decreasing this gapbetween the contacts to a distance equal to that of the device of Fig.l, a corresponding increase in operate time of the relay may be had.

Fig. 7 illustrates another embodiment having a single bimorph plate andin which two pairs of contacts are provided for alternate operation. Onepair of rear contacts 12a and 16a, of which 12a is centered on the rearsurface of plate 11, is placed so that when the plate is unstressed thecontacts are closed. The other pair of front contacts 12 and 16, ofwhich 12 is centered on the front face of plate 11, is placed so thatfor unstressed plate conditions these contacts are open. When the plateis stressed through application of an electric field, the rear contactpair opens and the front contact pair closes. Plate mounting and dampingand contact mounting and damping are as described for the device of Fig.1.

In Fig. 8 another embodiment of the invention is shown in which twopairs of contacts are provided for selective operation. In thisinstance, plate 41 is composed of two discs 42 and 43 of a ferroelectricceramic such as 4 per cent lead titanate barium titanate mixture ofwhich both plates are polarized in their thickness direction. Electrodesare evaporated on both sides of each disc and the discs, being orientedso that they are poled in the same direction, are sealed to form a plateaccording to the method described for the device shown in Fig. l. Theinner electrodes of the two discs are connected as a common electrodewhich along with the electrodes of the so that there is no rebound offof plate 11 is mounted, damped, .1

poled and subjected to an electric outside faces of the discs areconnected to a multiple power source 44. Two pairs of contacts 45 and 46are included, both pairs of which are open when the plate 41 isunstressed. The application of a field in one direction causes one pairof contacts to close and a field in the other direction causes theConductor pair 47 is connected to contact pair 46 while conductor pair48 is connected to contact pair 45.

Fig. 9 is a cross sectional view of a modification of the device of Fig.8 in which the damping contacts of contact pairs 45 and 46 are mountedfor movement on fiexure plates 51 and 52. A middle fiexure plate 41 isof the same construction as the device of Fig. 8. The fiexure plates 51and 52 are of the same construction as plates 26 and 11 of the device ofFig. 6. Flexure plate mounting and damping is as provided in the otherdevices. The electrodes of plates 41, 51 and 52 are connected to amultiple power source 44 so that plates 41 and 51 will in one instanceflex towards one another, closing the contact pair 46, and in anotherinstance plates 41 and 52 will flex towards one another closing contactpair 45.

it is to be understood that the described embodiments of the inventionand that other may be devised by those skilled in the art withoutdeparting either in spirit or scope from the invention herein set forth.

Vvhat is claimed is:

l. A relay comprising a mounting stand, a fiexure plate, said flexureplate being adapted to flex and change its curvature upon receivingelectrical energy, a first conductive electric contact mounted centrallyon said flexure plate, a second similar contact mounted on said stand,fiexure motion of said plate causing said first contact to move withrespect to said second contact along an axis normal to said fiexureplate at the center of said plate, a plurality of mounting springsattaching said plate to said stand, said mounting springs being spacedat substantially equal intervals around the periphery of said plate anddefining at their points of support on said plate a plane which changesin size and position as said plate flexes, each of said mountingrelatively rigid strip portion attached to the face of said fiexureplate and lying substantially in the plane of said plate, second andthird relatively rigid strip portions, said second portion beingintegral with and elastically hinged to said first and said thirdportions, said third portion being attached to said mounting stand, eachof said rnountin springs having all three strip portions in alignmentwith a plane including said axis along which said first contact moves,and means to reduce spurious mode vibrations in said flexure platecomprising damping means pressed against one face of said plate near itsedge.

2. A relay comprising a mounting stand, at least one electromechanicaltransducer bimorph fiexure disc, means to attach said disc to saidmounting stand at spaced points around the margin of said disc andcomprising a mounting spring at each of said points, said mountingspring comprising a rigid first portion attached to the face of saiddisc and extending radially outward therefrom beyond the periphery ofsaid disc, a rigid second portion that is integral with and elasticallyhinged to both said first portion and a rigid third portion that isattached to said mounting stand, at least one pair of conductive conbysharp bends, weakened at said bends to provide relative motion for saidportions.

mounting spring at each of said points, said mounting .spring comprisinga thin flat element having a rigid first portion attached to the face ofsaid disc and extending radially outward therefrom beyond the peripheryof said disc, a rigid second portion that is continuous with andelastically hinged to both said first portion and a rigid third portionat sharp bends where said spring is weakened, said third portion beingattached to said mounting stand, at least one pair of conductivecontacts, one contact of each pair being attached to the center of oneface of each said disc, the other contact of each pair being attached tosaid mounting stand, each said pair so spaced and arranged that theflexure motion of said disc will cause said contacts to open and close,and means to reduce spurious mode vibrations comprising bodies ofmechanically-lossy resilient material spaced around the margin of saiddisc between said three points and means to hold said bodies compressedagainst the face of said disc.

5. A relay comprising a mounting stand, at least one bimorph flexuredisc of effective piezoelectric elements, means to attach said disc tosaid mounting stand at spaced points around the margin of said disccomprising a mounting spring at each of said points, said mountingspring comprising a long thin flat element having a first rigid portionattached to the face of said disc and extending radially outwardtherefrom beyond the periphery of said disc, a rigid second portion thatis continuous with and elastically hinged to both said first portion anda rigid (F ii third portion at sharp bends which are weakened, saidthird portion being attached to said mounting stand, at least one pairof conductive contacts, one contact of each pair being attached to thecenter of one face of said disc, the other contact of each pair beingattached to said mounting stand, each said pair so spaced and arrangedthat the flcxure motion of said disc will cause said contacts to openand close, means to reduce spurious mode vibrations comprising bodies ofmechanically-lossy resilient material spaced around the margin of saiddisc between said three points and means to hold said bodies compressedagainst one face of said disc, and means to eliminate contact chattercomprising a body of energy dissipating material connected between saidmounting stand and each attached contact.

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